It has previously been known to use brake control systems on aircraft, such braking systems incorporating brake valves appropriately driven by a brake signal or error signal such as from an antiskid system, brake-by-wire system, or automatic brake control system. It has also been previously known to provide a redundancy of valve drivers for such systems to assure a continued operation in the event of a single failure. Typically, the redundant valve drivers operate totally independent of each other with only one of the valve drivers operating at a time, even when there has been no failure. Accordingly, the primary valve driver operates to solely provide the braking function until it fails, at which time the redundant circuit takes over full operation. The result is a heavy operational load on the primary circuit during normal operation. The temperature of the circuit increases and its life decreases.
Prior art systems have also been characterized by an interruption in operation at the time at which the redundant valve driver circuit is switched into operation to replace the failed primary valve driver. Because the primary and redundant circuits operate independent of each other, there is no smooth transition from the primary to the redundant circuit.
The prior art has also been found to require larger power supplies for driving the primary and redundant valve driver circuits since each operates exclusive of the other. The prior art circuits of this nature have been found to be current limited with respect to their power supplies unless significantly large power supplies are provided.